Attached is an extension which provides tabbed windows for IDLE. It supports drag-and-drop reordering and separate windows. 

The implementation relies on monkey-patching a few subroutines and duck-typing for the toplevel window. The extension emulates each tab as if it were its own toplevel object. 

There can be flickering when switching tabs due to swapping the toplevel menu bar. This seems to be a limitation of Tk.